ES2681669T3 - Apparatus and method for photopolymerization of digital flexographic printing plates - Google Patents

Abstract

An apparatus (1) for the photopolymerization of a flexographic printing plate (5), said plate (5) comprising a main face (5') and a base (5'') opposite said main face (5'), characterized because it comprises - an exposure chamber (20) comprising at least first photopolymerization means (21) of said base (5'') of said plate (5); - an input section (18) and an output section (19) for introducing/letting said plate (5) out of said exposure chamber (20), respectively; - moving means configured to drag said plate (5) along a feeding direction (101); wherein said first photopolymerization means (21) comprises a row of LEDs (21') aligned according to a direction substantially orthogonal to said feed direction (101), said photo-exposure chamber (20) comprises second means of photopolymerization (22) of said main face (5') of said plate (5), characterized in that said second means (22) comprise at least one row (31) of LEDs aligned according to a transverse direction (102) substantially orthogonal to said feed direction (101).

Description

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DESCRIPTION

Apparatus and method for the photopolymerization of digital flexographic printing plates Field of the invention

[0001] The present invention relates to the field of processes for the manufacture of digital flexographic printing plates. In particular, the present invention relates to an apparatus and method for the photopolymerization of digital flexographic printing plates.

Prior art

[0002] Flexography is a rotary direct printing method that uses embossed plates made of photopolymeric materials. The plates are flexible and soft, hence the name flexography. Said plates are dyed and the printing is obtained by means of direct deposition of the ink on the medium to be printed by virtue of a slight pressure exerted by a printing cylinder on which the plates are positioned.

[0003] Flexography is a high-speed printing process, capable of printing many types of absorbent and non-absorbent materials. Some typical applications of flexographic printing are the production of paper and plastic bags, milk cartons, disposable cups and the like, but by virtue of the progress of print quality, flexography is used today also for newspaper printing, for example, as well as packages and labels and for printing on plastic, films and sheets of acetate, wrapping paper and many other materials used for product packaging.

[0004] As is known, the prepress stage, that is the stage of preparation of the flexographic plate, which is subjected to various stages, one of which is the stage of exposing the plate to ultraviolet (UV) light for photopolymerization, It is very important and delicate.

[0005] To obtain the required embossed characters, the plate is polymerized only at the points of a mask left permeable to light. In the case of the so-called analog plates, a negative film is applied to the plate that shows the image to be printed in negative, while in the case of the so-called digital plates, the plates are covered with a layer that It is eroded by means of laser recording to create the negative image to be printed.

[0006] Exposing the plate to light causes polymerization only of the parts of the plate at the light permeable points of the negative film, in the case of analog printing plates or of the points at which the material layer Coated is eliminated in the case of digital printing plates, thus forming on the polymer the embossed image to be printed.

[0007] In all cases, the plate must be exposed to ultraviolet (UV) light for the necessary formation of the base (exposure of the back, that is to say the bottom or back of the plate). In the apparatus of the type known in the prior art, the main exposure stages, that is to say exposing the main face of the plate, and of the reverse exposure are generally performed within the scope of a continuous plate treatment process. Print. After the exposure stage, the flexographic plate is subjected to other processing steps, including the washing stage, by means of which the unpolymerized materials are removed from the plate.

[0008] It has been seen that the integration in the exposure of the plate, above all with respect to the exposure of the reverse, in a process of continuous treatment of the plate, determines a considerable complication in terms of design and control. At the same time, it has been found that inspection, maintenance and replacement of the means used for light curing are particularly complicated in a continuous process. A method and apparatus for the photopolymerization of flexographic printing plates that makes use of a plurality of LED lamps aligned along a direction transverse to the feed direction of the flexographic printing plate is disclosed for example in WO 2013 / 156942 A1. Thus, it is a main task of the present invention to provide an apparatus and method for the photopolymerization of flexographic digital printing plates that overcome the aforementioned drawbacks. In the scope of this task, it is a first object of the present invention to provide a compact, autonomous apparatus capable of autonomously carrying out at least photopolymerization of the secondary side of the reverse side. In the scope of this task, it is the object of the present invention to provide an apparatus capable of autonomously carrying out the photopolymerization of the main face and the secondary side of the reverse. It is a further object of the present invention to provide an apparatus that is reliable and easy to manufacture at competitive costs.

Summary

[0009] The present invention relates to an apparatus for the photopolymerization of a flexographic printing plate comprising a main face and a base opposite to said main face. The apparatus is characterized in that it comprises an exposure chamber provided with at least first light-curing means of the

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plate base. Said apparatus further comprises an input section and an output section for introducing / letting out the sheet of said exposure chamber, respectively. The apparatus further comprises movement means configured to drag said plate along a feed direction. According to the invention, said first photopolymerization means comprise a row of LEDs aligned in accordance with a direction substantially orthogonal to the feed direction. The device according to the invention is also provided with a second light-curing means of the main face of the flexographic printing plate. Said second light-curing means comprise a row of LEDs aligned in accordance with a direction substantially orthogonal to the feeding direction.

[0010] The apparatus according to the invention allows simultaneous photopolymerization of the base and the main face of the plate.

[0011] Said apparatus can be advantageously totally autonomous, that is to say totally disconnected from the other treatment operations normally performed on flexographic plates.

List of figures

[0012] The additional features and advantages of the present invention will become more apparent from the detailed description that follows provided by way of non-limiting example and shown in the accompanying drawings, in which:

- Figure 1 is a schematic general view of a first embodiment of an apparatus according to the present invention;

- figure 2 is a detail view of the change of exposure of the apparatus of figure 1;

- Figure 3 is a schematic view of the components of the apparatus of Figure 1;

- Figure 4 is a block graph relating to the control of an apparatus according to the present invention;

- Figure 5 is a schematic view of a second embodiment of an apparatus according to the present invention;

- Figures 6 to 8 are schematic views of the components of an apparatus according to the invention.

[0013] The same parts and the same corresponding components are indicated in the figures with the same reference numbers.

Detailed description

[0014] The apparatus according to the invention is indicated as a set by reference number 1 in the mentioned figures. The apparatus 1 can be used for the photopolymerization of a flexographic printing plate 5. Said plate 5 comprises a main face 5 'and a base 5' 'opposite the main face 5'. The apparatus 1 according to the invention is configured to carry out, preferably autonomously, at least the photopolymerization of the base 5 '' of the plate 5.

[0015] The apparatus 1 according to the invention comprises at least one exposure chamber 20 comprising at least first photopolymerization means 21 configured to carry out the photopolymerization of said base 5 ''. Hereinafter, the light curing operation of the base 5 '' will also be indicated by the term "REVERSE exposure". The apparatus 1 further comprises an input section

18 and an output section 19 for inserting / letting out said plate 5 from said exposure chamber 20, respectively.

[0016] The apparatus 1 comprises means of movement of the plate 5 that interact with it. More precisely, the movement means define a feed direction 101 for the plate 5 in the exposure chamber 20. According to a first possible embodiment, the inlet section 18 and the outlet section 19 are defined by opposite sides 20 ', 20' 'of the exposure chamber 20. In this configuration, the feed direction 101 preferably comprises a single rectilinear feed segment between the input section 18 and the output section 19.

[0017] According to an alternative embodiment (not shown), the input section 18 and the output section

19 are defined on the same side of the exposure chamber 20.

[0018] According to this alternative embodiment, the movement means of the plate 5 define a movement path within the exposure chamber comprising a first section and a second section. The first section develops between the inlet section towards a first side 20 '' of the chamber 20 opposite the first side 20 'to a predetermined position. The second section is developed from said predetermined position towards the first side 20 'of the chamber 20, that is to the exit section 19. In this alternative embodiment, the movement means of the plate 5 will be configured to pass the plate 5 from the first section to the second section in said predetermined position.

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[0019] In practice, the movement means reverse the feed direction of the plate 5.

[0020] As will be described in greater detail below, the movement means of the plate 5 are electrically connected to a control unit 90 that determines their operation.

[0021] In this regard, first detecting means 201 connected to the control unit 90 are arranged in the input section 18. Second detector means 202 are preferably provided in the output section 19. Said second detector means 202 are also connected to the control unit 90. The latter activates and deactivates the movement means based on the corresponding signals received from said detector means 201, 202.

[0022] The apparatus 1 further comprises a flat structure 6 defining a preferably horizontal resting plane 105 (in Figure 2) for the base 5 '' of the plate 5. In this sense, said base 5 '' can rest or either directly or indirectly on said plane 105. Actually, the sheet 5 can be mounted on a support layer 5 '' made of transparent material. In this state, the support layer 5 '' of the plate, and not the base 5 '', rests directly on the rest plane 105.

[0023] The sliding base 6 comprises a transparent zone 66, preferably made of glass, to allow the transmission of the light radiation emitted by the first light-curing means 21. A second zone 66 'of the sliding base 66 can be manufactured. instead of metallic material, for example aluminum. The apparatus 1 preferably comprises cooling means of the second zone 66 'of the flat structure 6.

[0024] The first means 21 are preferably operatively connected in place under the flat structure 6 and more precisely in place below the transparent position 66 of the flat structure 6. In this case, the plate 5 is inserted into the exposure chamber 20 through the input section 18 so that the base 5 '' faces downwards, that is to the floor 300 on which the structure 250 of the apparatus 1 supporting the exposure chamber 20 rests. input section 18 and output section 19 are advantageously configured so as to allow treatment of plates with different widths L, evaluated along an orthogonal direction to the feed 101 (see figures 6 through 8) .

[0025] As shown in Figure 1, the sheet 5 can be approximated to the entrance section 18 by means of a trolley 3 or functionally equivalent means. At the exit of the exposure chamber, the plate 5 can be wound thanks to its flexibility and transported for further treatment. The apparatus 1 can thus be totally independent of the online process.

[0026] With reference to Figures 2 and 3, according to the invention, the first light-curing means 21 comprise at least one row of LED elements 21 'aligned in accordance with a transverse direction 102 substantially orthogonal to the feed direction 101 Said first means 21 further comprise first brightness adjustment means 7, of the brightness of said LEDs. Said first means 21 also preferably comprise a first support module 12 of said LEDs.

[0027] According to a further aspect, the apparatus 1 according to the invention comprises first means for adjusting the distance 8 for adjusting the distance between said first light-curing means 21 and the glass area 66 of the flat structure. 6 on which the plate 5 rests. In particular, said distance can be varied depending on the type and thickness of the plate 5 that crosses the exposure chamber 20. The first distance adjustment means 8 can be manually operated or electronically operated. This indicates the possibility of connecting said means to the control unit 90 of the apparatus, as shown schematically in Figure 4.

[0028] With reference to Figure 5, the apparatus 1 also comprises second light-curing means 22 for the "MAIN exposure" of the plate 5, this term indicating the light-curing operation of the main face 5 'of said plate 5. Said second means 22 are installed in opposition to the first photopolymerization means 21 with respect to the rest plane 105. In summary, the second means 22 are installed in a position above the rest plane 105, that is to say on the plate 5 that transits in the exposure chamber 20.

[0029] The second light-curing means 22 comprise at least one row of LED 31 aligned in accordance with a direction that is substantially orthogonal to the feed direction 101. The second means 22 preferably comprise a plurality of rows 31, 32, 33, 34 of LEDs parallel to each other and arranged at a predetermined distance D evaluated according to a direction parallel to that of power 101. Each row of LED 31, 32, 33, 34 is oriented so that it is orthogonal to the power direction 101 Said second light-curing means 22 preferably comprise additional brightness adjustment means 77 for adjusting the brightness of said LEDs.

[0030] Said additional brightness adjustment means 77 are also electrically connected and controlled by the control unit 90 of the apparatus 1, as schematically shown in Figure 4. In this sense, the control unit 90 can intervene by means of the Adjusting the intensity of the LEDs in each row independently of the other rows.

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[0031] The second light-curing means 22 preferably comprise at least a second support module 11 adapted to support said rows of LEDs. Said second module 11 can be configured to support one, some or even all said LED rows. In the embodiment shown in Figure 5, for example, a second module 11 is provided which supports four rows 31, 32, 33, 34 of LEDs arranged in place above the rest plane 105. Said rows 31, 32, 33 , 34 are equidistant distantly along a direction parallel to the feed direction 101. It is worth noting that the number of LED rows may vary according to the cases. For example, the rows of LEDs drawn with a dashed line in Figure 5 and indicated with reference numbers 33 and 34, can either be installed or not according to the quality and depth required for the main exposure.

[0032] According to another aspect of the present invention, said at least one row of LED 21 'of the first means 21 is coplanar with at least one row of LED 31 of the second means 22. More specifically, said at least one LED row 31 of the first means 21 and said at least one LED row define a reference plane 500 that is substantially orthogonal to the feed direction 101 of the plate and / or the rest plane 105 (i.e. the structure flat 6) of the plate 5.

[0033] Preferably, each LED of said first light-curing means 21 is aligned with a corresponding LED of said second light-curing means 22 along a direction that is coplanar with said reference plane 500 and orthogonal to said power plane 102 It has been seen that this condition has a synergistic effect with respect to the definition of the profile of the parts of the plate 5 that are polymerized. In other words, it has been seen that the alignment of the LEDs that carry out the reverse exposure with the corresponding LEDs that carry out the main exposure improves the definition of the parts polymerized in part by means of the main exposure.

[0034] Again with reference to the aforementioned figure 5, the apparatus preferably comprises air cooling means 14 configured to cool the main face 5 'of the plate during the MAIN exposure. The second photopolymerization means 22 also preferably comprise second distance adjustment means 88 for adjusting the distance from the rest plane 105. Said means can be activated manually or electrically controlled, for example by means of the control unit 90, as schematically shown in figure 4.

[0035] The apparatus according to the invention preferably comprises attenuation means configured to prevent reflection of the second light-curing means 22 of the light generated by the first light-curing means 21. More precisely, said attenuation means have the function of prevent the light generated by the means used for the MAIN exposure from being diffused under the plate 5 thus disturbing the diffusion of the light generated by the means used for the REVERSE exposure.

[0036] Figures from 6 to 8 show a possible embodiment of said attenuation means. Said figures 5 are substantially schematic views taken along a section plane XX indicated in figure 1. In said figures, the rest plane 105 is shown with the area of transparent material 66 and the first exposure means 21 provided for carry out the REVERSE exhibition. The attenuation means preferably comprise two curtain elements 116 arranged on opposite sides with respect to the plate 5. Said curtain elements 116 are configured to cover / dim the LEDs (indicated by reference number 21 '') of the first means 21 that are not above the plate 5 during transit of the plate in the exposure chamber 20. In other words, according to the invention, the extent of the attenuation means is adjustable depending on the width L of the plate and along a transverse direction 102 substantially orthogonal to the feed direction 101 of the plate itself.

[0037] In summary, the succession of the curtain elements 116 is adjustable and is determined as a function of the width L of the plate 5, as can be deduced from the comparison between Figures 7 and 8. In Figure 7, the elements of Curtain 116 has an extension L, measured along an orthogonal direction to the feed direction, which is greater than that of the same elements of Figure 8 in which the plate has a width greater than that of Figure 7. The possibility of using other attenuation means functionally equivalent to the curtain elements 116 described above and shown in the figures is naturally within the scope of the present invention.

[0038] According to another aspect of the present invention, the movement means of the plate 5 in the exposure chamber 20 preferably comprise at least one pair of first drive rollers 51 installed in a position close to the inlet section 18 and a pair of second drive rollers 52 installed in a position close to the output section 19. For each pair, the rollers 51, 52 are installed in opposite positions with respect to the rest plane 105 of the plate 5 and so that its axis of rotation 150 is substantially orthogonal to the feed direction 101. The distance between two opposite rollers is set so as to generate a pressure on a plate sufficient to determine the drag thereof. For each pair, the rollers are preferably coated externally with soft rubber.

[0039] For each pair, at least one of said rollers 51, 52 is connected to controlled motor means, in turn, by the control unit 90 depending on the position of the plate 5 in the exposure chamber 20 and by it in

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function of the signals sent by the first detector means 201 and the second detector means 202 indicated above. The speed of rotation of the rollers 51, 52 is set according to the characteristics required by the photopolymerization process.

[0040] As mentioned in various passages of the description, the control unit 90 is thus provided to control almost all components of the apparatus 1 according to the invention. The control unit 90 is provided with user interface means 91 that allow an operator to intervene by modifying the operating parameters, which are for example: the distance and intensity of the polymerization means and / or the feed rate of the plate 5. Depending on these parameters and the position of the plate 5 in the exposure chamber 20, the control unit 90 will, accordingly, control the first polymerization means 21, the second polymerization means 22, the movement means (rollers 51, 52), the cooling means 14 of the plate 5, the cooling means 19 of the flat structure 6 and the cooling system 17 of the light-curing means 21, 22.

[0041] From the foregoing, it is clear that the present invention also relates to a method for the photopolymerization of a plate that allows the main exposure and the reverse exposure to be carried out simultaneously. The method according to the present invention includes providing an exposure chamber and dragging the plate into the chamber according to a feed direction. The method according to the invention includes carrying out the photopolymerization of the base (reverse exposure) of the plate in the exposure chamber by means of first photopolymerization means comprising a row of LEDs arranged according to a direction orthogonal to said feed direction. The method according to the invention includes carrying out the photopolymerization of the main part (main exposure) of the plate in the exposure chamber by means of the second light-curing means comprising a row of LEDs that are arranged / oriented according with an orthogonal direction to the feeding direction.

[0042] According to a first aspect, the method includes carrying out the main exposure by means of a plurality of rows of LEDs arranged so that they are parallel to each other and so that each one is aligned / oriented accordingly. with a direction substantially orthogonal to said feed direction.

[0043] According to another aspect, the method includes the provision of a row of LEDs provided for the main exposure and a row of LEDs provided for the reverse exposure so that the two rows are coplanar on an orthogonal reference plane to the feed direction of the plate in the exposure chamber. Each of the LEDs used for the reverse exposure is preferably aligned with a corresponding LED used for the main exposure along a direction that is coplanar with the reference plane indicated above. As already indicated above, this arrangement advantageously allows to improve the definition of the light-cured parts by means of the main exposure.

[0044] It is worth noting that the method according to the invention can be implemented within the scope of an autonomous apparatus as described above, but also within the scope of a more complex system in which other treatment operations are performed in addition to of light curing.

Claims (14)

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Five fifty 55 60 65 An apparatus (1) for the photopolymerization of a flexographic printing plate (5), said plate (5) comprising a main face (5 ') and a base (5' ') opposite to said main face (5') , characterized by comprising - an exposure chamber (20) comprising at least first photopolymerization means (21) of said base (5 '') of said plate (5); - an input section (18) and an output section (19) for inserting / leaving said plate (5) of said exposure chamber (20), respectively; - movement means configured to drag said plate (5) along a feed direction (101); wherein said first photopolymerization means (21) comprises a row of LEDs (21 ') aligned in accordance with a direction substantially orthogonal to said feed direction (101), said photo-exposure chamber (20) comprises second means of light curing (22) of said main face (5 ') of said plate (5), characterized in that said second means (22) comprise at least one row (31) of LEDs aligned in accordance with a transverse direction (102) substantially orthogonal to said feed direction (101). 2. An apparatus (1) according to claim 1, wherein said apparatus (1) comprises a flat structure (6) on which said base (5 '') rests either directly or indirectly, said structure comprising flat (6) a transparent zone (66), said first photopolymerization means (21) being located in a position below said transparent zone (66). 3. An apparatus (1) according to claim 1 or 2, wherein said movement means comprise at least one pair of first drive rollers (51) installed in a position close to said inlet section (18) and a couple of second drive rollers (52) installed in a position close to said exit section (19), in which for each of said pairs, the rollers (51, 52) are installed in an opposite position with respect to a feed plane of said plate (5) and so that the axes of rotation (3 ) thereof are coplanar with a plane substantially orthogonal to said feed direction (101). 4. An apparatus (1) according to claim 2 or 3, wherein said apparatus comprises means for cooling said flat structure. An apparatus (1) according to claim 1, wherein said second means (22) comprise a plurality of rows (31, 32, 33, 34) of LEDs aligned in accordance with a substantially transverse direction (102) orthogonal to said feed direction (101). An apparatus (1) according to claim 1, wherein at least one row (31) of LED of said second means (22) and at least said row of LED (21 ') of said first means (21 ) are coplanar with a reference plane (500) substantially orthogonal to said feed direction (101). An apparatus (1) according to claim 6, wherein each of the LEDs of said at least one row (31) of LEDs of said second photopolymerization means is aligned with a corresponding LED of said first means ( 21) according to a coplanar direction with said reference plane (500). 8. An apparatus (1) according to any one of claims 1 to 7, wherein said apparatus comprises brightness adjustment means (7) for adjusting the brightness of said LEDs of said first means (21 ) and / or distance adjustment means (8) for adjusting the distance of said LEDs of said first means (21) from said base (5 '') of said plate. 9. An apparatus (1) according to any one of claims 1 to 8, wherein said apparatus comprises brightness adjustment means (77) for adjusting the light intensity of said LEDs of said seconds means (22) and / or distance adjustment means (88) for adjusting the distance of said LEDs (31, 32, 33, 34) of said second means (22) from said main face (5 ') of said plate (5). 10. An apparatus (1) according to any one of claims 1 to 9, wherein said apparatus comprises attenuation means configured to prevent reflection, on said second light-curing means (22), of the light generated by said first photopolymerization means (21). 11. A method for the photopolymerization of a flexographic printing plate (5), wherein said plate (5) comprises a main face (5 ') and a base (5' ') opposite to said main face (5') , wherein said method comprises the steps of: - prepare an exposure chamber (20); - dragging said plate (5) into said exposure chamber (20) according to a direction of feeding (100); - carrying out, in said exposure chamber (20), the photopolymerization of said base (5 '') of said plate by means of first photopolymerization means (21) comprising a first row of LEDs aligned in accordance with a direction orthogonal to said feed direction (100); 5 - carrying out, in said exposure chamber (20), the photopolymerization of said main face (5 ') of said plate (5) by means of second light-curing means (22) comprising at least one row (31) of LEDs aligned in accordance with an orthogonal direction to said feed direction (100). 12. A method according to claim 11, wherein said method includes carrying out the Light curing of said main face (5 ') of said plate (5) by means of a plurality of rows (31, 32, 33, 34) LED by arranging said rows (31, 32, 33, 34) parallel to each other and so that each one is aligned in a direction substantially orthogonal to said feed direction. 13. A method according to claim 11 or 12, wherein said method comprises the step of arranging said at least one row (31) of LEDs of said second means (22) and said at least one row (21 ' ) of said first means (21) so that the LEDs of the two rows (31, 21 ') are coplanar with a reference plane (500) orthogonal to the feed direction (100). 14. A method according to claim 13, wherein said method comprises the step of arranging said 20 minus one row (31) of LED of said second means (22) and said at least one row (21 ') of said first means (21) so that each LED of said first row (31) of LED of said second means (22) is aligned with a corresponding LED of said row (21 ') of LED of said first means (21) in accordance with a coplanar address to said reference plane (500).